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Sheep Ked Fly

The sheep ked, Melophagus ovinus, a wingless, bloodsucking fly is often misnamed the "sheep tick" because it resembles a large tick. However, as with the other members of the class Insecta, the sheep ked features only six legs and not the requisite eight of the ticks and fellow arachnids.

Although they occasionally bite humans and exhibit some success on goats, this flat, leathery, reddish-brown insect feeds almost exclusively on sheep. Well adapted for blood meals, the head is characterized by a noticeable piercing mouthpart that projects forward. Without a blood meal, the 4- to 7-millimeter keds perish within four days, but an engorged female can last up to eight days seeking a new host. In young lambs, these wingless flies can cause anemia and with adult sheep, retard weight gain. Keds and their pupae, when found in harvested wool, result in a "dirty wool" classification. Because of the sheep's negative immune response to the feeding keds, wool production also suffers.

Exhibiting complete metamorphosis, M. ovinus has a pupal stage that lasts for 3 to 6 weeks. The larval stage undergoes two molts while still within the mother. By the end of the growth period for the third instar stage, the female releases the larva on the host sheep (to pupate) and secures the future of the progeny by cementing them onto the wool. Eggs hatch one at a time instead in an episodic event. It takes about one or two months for the sheep ked to complete its life cycle. Because transmittal is due to sheep-to-sheep contact in flocks, isolation and shearing of infected livestock is prescribed, along with treatment by organophosphate insecticides or ivermectin. In the United States, sheep keds have virtually been eliminated through effective quarantine and treatments.